Aim: How does light provide evidence of the universe’s composition?

I. Light – a form of electromagnetic radiation.

A. electromagnetic radiation – energy that travels in waves. (examples – radio waves, x-rays, gamma rays)

B. Each wave type travels at the speed of light (300,000 km/sec or 186,000 miles/sec.)

Crest1 wavelength

C. Electromagnetic spectrum – a continuum of electromagnetic radiation. (Go to page 14 of ESRT)

Increasing wavelength

Increasing energy

1. Visible white light – is made up of various colors, each with a different wavelength. (Red light has the longest wavelength and the least amount of energy. What about violet light?)

a. Spectroscope – used to break up light from an object.

b. Different elements give off different wavelengths

c. Astronomers can determine what stars and planets are made of by the light waves they emit or absorb.

D. Doppler Effect – the apparent change in the wavelength of radiation or a sound in which there is relative motion between the source and the receiver.

1. Red shift – when wavelengths are increasing, giving evidence that the object is moving away from the observer.

2. Blue shift – when wavelengths are decreasing, giving evidence that the object is moving towards the observer.